The
Third Stage of Recovery.The third stage of recovery is characterized
by the death of the parasite, after which a fibrotic reaction ensues
and the cyst disappears (Fig. 22.35). Once diagnosed, paragonimiasis
can be effectively treated with oral praziquantel, with a cure rate
of 70% with one day therapy, and 90 to 100% with 2 and 3-day therapies
(Shim et al 1991)(Fig. 22.22).
The drug's mechanism of action is not completely elucidated.

......

Fig. 22.35A-C.
Paragonimiasis in a Korean man showing slight progressive healing of
the small cystic lesions at the right lung base on serial chest films
taken over a 1 year period. (A) PA chest film and (B)
coned view of the right lower lung show a few small cysts with surrounding
exudative reaction and tortuous worm burrows in the adjacent parenchyma.
There are also small 1-cm ring-like shadows in the right upper lobe
and suprahilar area (arrows). (C) A view of the right
lower lung from a chest radiograph taken 11 months later shows the chronicity
of the Paragonimus lesions, with slight change in the interval.
Some of the surrounding exudative reaction has disappeared and has gradually
been replaced by fibrosis. Note the horizontal linear strands extending
to the overlying pleura along the lower lateral chest wall. Paragonimus
cysts are commonly found in a peripheral or subpleural location and
often show an overlying localized pleural reaction or linear stranding
to the pleura as seen here. This patient was a 38-year-old North Korean
with jaundice, generalized weakness, and right chest and hypochondrial
pain that increased on deep breathing. He had a productive cough and
his sputum contained P. westermani eggs, but no blood.

However,
it increases the permeability of the integument to the calcium ion,
immediately triggers the extreme contraction of the worm, and results
in paralysis of the worm followed by lysis. The clinical symptoms and
signs of the disease may totally disappear and the chest radiograph
may eventually show either no residual lesions or irregular fibrotic
linear opacities radiating into the surrounding pulmonary parenchyma.
The time required for radiological resolution depends on the chronicity
of the lesions; chronic lesions last longer and leave more fibrotic
lesions after successful treatment. Fibronodular opacities may eventually
resorb and calcify. These calcifications range from 2 to 5 mm in diameter
and may closely resemble those of healed tuberculomas on plain radiographs
and CT scans (Figs. 22.36, 22.37). However, unlike in cerebral
paragonimiasis and pulmonary tuberculosis, calcification is uncommon
in pulmonary paragonimiasis (Im et al, 1992). Because tuberculosis is
widespread in the endemic areas where paragonimiasis is found, small
pulmonary calcifications may represent healed lesions of either, or
both, diseases.

...

Fig. 22.36 A, B. The
stage of recovery in pulmonary paragonimiasis is characterized by fibrosis
and small calcifications ranging from 2 to 5 mm in size, as illustrated
in these coned views of the midlung fields of two Korean men. P.
westermani eggs were found in the sputa of both patients. In patient
(A), there is a large aggregate of small ring shadows and cysts
in the right midlung, each cyst measuring 1 cm or less. The cyst walls
are well defined and thin. A corona effect produced by a crescent-shaped
density in the lateral wall of the most lateral cyst (arrow)
identifies the characteristic ring shadow of paragonimiasis. As these
second stage lesions heal, the chest radiograph may show small homogeneous
densities with fibrous cords radiating into adjacent pulmonary parenchyma.
These densities may resorb with deposition of calcium, as seen in this
patient, who has two small calcifications lateral to the hilus. (B)
Another patient with small cystic lesions in the lateral aspect of the
midlung as well as multiple 5 mm calcifications in the upper lobe and
hilar region. Such calcifications are also seen in healed tuberculosis,
and indeed the two diseases may coexist in the same individual since
they are endemic in the same countries, especially in the Orient.

Fig. 22.37. Chronic
pulmonary paragonimiasis in a 61-year-old Korean man presenting with
calcified nodules in the lung. High-resolution CT shows 4 to 5-mm aggregated
nodules in the right upper lobe containing calcifications. Calcification
in pulmonary paragonimiasis is uncommon, but can occur in cases of chronic
untreated lesions, as in this patient. P.
westermani ova were found in needle aspirates of the right lung
lesion. The patient was successfully treated with oral praziquantel;
however, the calcified small nodules remained unchanged.